The present invention relates to Tonneau Covers, particularly Tonneau Covers including a flexible cover and an apparatus for attaching the flexible cover to a cargo box of a pick up truck; the apparatus including a rear bar or end plate and end plate engagement members cooperating to impart tension to the flexible cover when the end plate pivots into or is positioned in a closed position with respect to the end plate engagement members and a locking member or members preventing unauthorized detachment of the end plate from the end plate engagement members.